A number of standard radio specifications are currently being proposed for UWB radio communications. One example is the MBOA (MultiBand ODFM Alliance) specification.
At least some UWB specifications, such as MBOA, define a beacon signal that is transmitted at regular intervals. This beacon is used to help keep the radios of multiple devices synchronized and to allow additional devices to form a connection with the device transmitting the beacon. The beacon signal incorporates a number of items of information, including a local device address and a global device identifier. The local device address is negotiated locally with any other devices within listening range while the global device identifier remains constant and is globally unique to the device transmitting the beacon signal.
The local device address and the global device identifier are of different lengths; the longer, constant global address identifier is transmitted in the beacon to allow a device entering the network to determine which other device it wants to communicate with. It is essentially equivalent to a MAC address. For example, a mobile phone might want to connect to a printer and might know from past experience that the printer has a certain address. When the phone is brought into a UWB network, it could then look for the device having that address in order to perform printing. The global device identifier needs to be sufficiently long that all UWB devices operating according to the protocol can have their own unique global device identifier.
The local device address is shorter and is negotiated locally. It is used in packets within a frame (the sub-divided period between beacons) to identify which device that individual packet is from and/or which device it is addressed to. The reason for using a separate identifier from the global device identifier for this purpose is that the global address identifier is excessively long to use in every single data packet and would consume unnecessary bandwidth if it were used for this purpose. The local device address only needs to be sufficiently long that it can uniquely identify a device from the maximum number of devices than would practically be connected together at any one moment.
A UWB radio device operating in this way would be continuously transmitting its beacon signal. Since this signal contains a constant, unique identifier, the UWB-enabled device could be tracked by any interested party. This represents a loss of privacy for the owner of such a device. This is especially acute if the device in question is a personal mobile device (i.e., a device of the sort that a user might be expected to carry with them when they are out and about). Examples of such devices include mobile phones, digital cameras, music players, PDAs and watches.